Soil Amplification Factors Research Articles

Characterization of Site Amplification by a Parametric Study

ABSTRACT The reliability of V s30 and the performance of alternative time averaged shear wave velocities (V sz ) and shear wave travel times (T tz ) at various depths, z, were investigated for the estimation of site amplification and fundamental frequency (f 0) characterization by considering the linear and nonlinear soil behavior. The study revealed that alternative parameters performed better than V s30 and the best performing z parameters changed by switching from convex to concave theoretical profiles and by increasing ground motions. For a practical usage in site investigations, guidelines to estimate nonlinear soil amplification factor and fundamental frequency from the linear ones were presented.

Earthquake response of historical church within the perspective of structural dynamics: Oltu Russian Church

Structural dynamic feature studies are increasingly applied as an important activity in assessing the vulnerability of cultural structures and identifying the possible damage mechanisms. The modal parameters of the building and soil dynamic properties have been obtained by several methods to assess the structural behavior of the Oltu Russian Church in this study. The H/V curves obtained from the microtremor results applied in the churchyard and inside the church show that the average soil dominant frequency is ∼3 Hz. The soil amplification factor values are calculated as ∼3 and ∼2.5 for the inside and outside of the church, respectively. The slip-strain value calculated in the light of microtremor results shows that the soil dynamic behavior can be elastoplastic in the design earthquake. A finite element model of the Oltu Russian Church is established with soil, modal parameters, and material information obtained from the field under the influence of a series of earthquake data. The response spectra of the domed and non-domed structures have been scaled and matched against these designed earthquakes with the horizontal elastic acceleration spectrum for the structure. It is concluded that the restoration of the domes increased the acceleration values in the towers. The application of restoration processes on the domes caused approximately 10 times more displacement. It has been observed that the average impacting earthquake structure has a 1st mode frequency of 0.7 Hz, a 2nd mode frequency of 1.8 Hz, and a 3rd mode frequency of 2.5 Hz.

Seismic Vulnerability Analysis Using the Horizontal to Vertical Spectral Ratio (HVSR) Method on the West Palu Bay Coastline

This research was carried out to make a map of the dominant frequency (f0), amplification factor (A0), seismic susceptibility index (Kg), Vs30, Sediment Layer Thickness (H) and Peak ground acceleration (PGA). Microtremor measurements were carried out with a three-component seismometer of the TDL-303S type as many as 27 measurement points. The data was analyzed by the Horizontal to Vertical Spectral Ratio (HVSR) method. The PGA calculation was carried out using the Kanai equation with a reference to the Palu-Donggala earthquake on September 28, 2018. The results showed that the distribution of the dominant frequency value (f0) ranged from 0.4149 Hz-0.8869 Hz, the soil amplification factor (A0) ranged from 2,199–4,884, the seismic vulnerability index (Kg) ranged from 8.79 s2/cm-41.41 s2/cm, the shear wave velocity to a depth of 30 meters ( Vs30) ranged from Vs30 197.7 m/s-320.2 m/s , the thickness of the sedimentary layer ranges from 260.3 m-291.1 m and the peak ground acceleration (PGA) of Kanai ranges from 137.3 gal – 234.2 gal by using Mw 7.4 earthquakes with an intensity scale (MMI) VI to VII. The coastal area of West Palu bay has an intermediate seismic vulnerability II to a high seismic vulnerability IV so that it will be vulnerable in the event of an earthquake disaster. Areas that have a very high vulnerability index are in the upper western and easternmost regions while those with a lower level tend to have a lower vulnerability index value.

Preliminary System for the Estimation of Peak Ground Acceleration Distribution in Metropolitan Lima and Callao: Application in Recent Seismic Events

The conjunction of seismic records and site effect parameters can lead to the adequate estimation of seismic indexes in urban areas. In this regard, this study uses the map of soil amplification factors obtained in previous studies and the availability of time history waveforms at different locations throughout Metropolitan Lima and Callao to estimate the geospatial distribution of maximum values of horizontal acceleration after the occurrence of earthquakes. Results for three earthquakes of intermediate magnitude and distinct epicenter locations are publicly available in an online system created within the framework of this study (Amaru Peru) and showed that amplified motions could be mainly observed in the lowlands of populated slopes as well as in the eolian sandy deposits.

PROPOSAL OF SEISMIC LOAD FOR TRADITIONAL HOUSES IN KYOTO

In this paper, first, an approximation formula for the amplification factor of the surface soil is proposed. However, since most of the traditional houses are located on good soil condition, the lower limit of surface soil amplification factor 1.23 may be acceptable in reality. On the other hand, the large amplification sites are hardly related to the large shaking area during the Hanaore-fault-zone earthquake which is deeply related to the safety of traditional houses in Kyoto. We also pointed out that increase in bearing capacity of houses may increase the deformation response in case of pulse-like ground motion input.

EVALUATION OF SURFACE SOIL AMPLIFICATION FACTOR FOR SEISMIC DESIGN IN KYOTO CITY AREA

Based on the analysis results of the seismic diagnosis design of traditional houses in Kyoto, it has been considered that the surface soil amplification factor indicated in the guidelines may be overestimated. In this paper, we have analyzed the soil model used in the calculation of the amplification factor in the guidelines and that used in the earthquake damage estimation in Kyoto. As a result, the former soil model is not adequate for Kyoto city area. In addition, the lower limit of 1.23 is sufficient for the amplification factor used in the seismic diagnosis of traditional houses.

Analysis of reinforced soil wall for c–ϕ backfill considering Rayleigh wave

Analytical methods to analyse the seismic stability of reinforced soil walls showing the effect of Rayleigh waves are not available to date. In this study, the pseudo-dynamic approach was used to determine the seismic behaviour of a reinforced soil wall considering the propagation of primary, shear and Rayleigh waves. A mathematical derivation is proposed to obtain the required strength of reinforcements, the critical angle of the failure wedge and the factor of safety (FS) of the reinforced soil wall. The non-linear distribution of tensile force in the reinforcements can easily be obtained for the case of c–ϕ backfill using the results from the present parametric study. A sizable effect of horizontal ground acceleration and soil amplification factor on the required strength of reinforcements, critical angle of failure wedge and FS was observed. The trends found for Kmax and FS clearly emphasise the prominence of Rayleigh wave consideration in the analysis.

Seismic Microzonation Map for a Fixed-Jacket Platform in the Malay Basin

The existence of soft soil in offshore areas may lead to the amplification of vibration received from offshore facilities, especially from the existing fixed-jacket platforms, which were designed without provision to seismicity, as in Malaysian water. Therefore, this study was designed to develop a seismic microzonation map and a soil amplification factor map according to soil type; we propose horizontal response spectra and site coefficient values (Ca and Cv) for the Malay Basin. A one-dimensional nonlinear analysis of layered soil (NERA) was used in the ground response analysis for six selected seismic events under five return periods of 100, 200, 500, 1000, and 2500 years. Soil amplification factors for soil types D and E showed a decreasing trend from 100 years to 2500 years. Two designed horizontal response spectra are proposed (for soil type D and E) under average and envelope conditions; a comparison with ISO showed that the proposed spectra were higher, especially for soil type E. To summarize, the seismicity effect should be included in the development of offshore industries as findings indicated that soil amplification occurred in soil types D and E at the Malay Basin.

Influence of soil amplification and backfill angle on seismic earth pressure coefficients by pseudo dynamic method

ABSTRACT The knowledge of earth pressure concepts plays a major role to design a retaining wall. The most traditional pseudo-static methodology as proposed by Mononobe–Okabe gives the direct approximation of earth pressure in seismic condition. This paper utilised the pseudo-dynamic methodology to figure out the seismic earth pressure on rigid wall with cohesion less backfill along with considering the effects of time, phase difference, soil amplification factor along with the variation in seismic velocities. The main contribution is the soil amplification and backfill inclination which is not given much attention before. By considering the above factors coefficients the seismic earth pressure against retaining wall is determined. The coefficient of seismic passive earth pressure decreases with the increase of soil amplification keeping other properties as standard values. The value of coefficient of seismic active earth pressure increases with increase of soil amplification. The comparison is also done without taking backfill angle for both coefficients of seismic earth pressures. The influence of all the soil properties like backfill angle, wall friction angle, soil friction angle, non-dimensional parameters are shown in tabular format as well as in the graphical with respect to the soil amplification which is more realistic towards the design.

Site-specific seismic hazard levels at the economic zone of Duqm, Oman

AbstractA site-specific probabilistic seismic hazard assessment (PSHA) was achieved in the area of special economic zone authority of Duqm, involving hazard evaluation at the bedrock conditions and assurance of potential site influence on seismic ground motion at the bedrock. Appropriate source and ground-motion prediction models were selected and seismic hazards were identified by means of 5% damped Uniform Hazard Spectra (UHS) for three return periods of 475, 975, and 2475 years. A logic-tree algorithm was used to study the influence of the epistemic uncertainties on the source models, earthquake recurrency and maximum magnitude, along with ground-motion prediction equations (GMPEs). The local geology effects were characterized by fundamental resonance frequency (Fo) using the horizontal-to-vertical spectral ratio technique and the soil amplification factors. The effects of soil were assessed using SHAKE91 for soil parameters defined by 55 geotechnical boreholes in conjunction with surveys of 2D multichannel analysis of surface waves (MASW) at 90 sites. Scaling was performed for selected strong-motion applying spectral matching technique to be used at the soil column bottom. Selection of such records is based on scenarios characterized by deaggregation of the PSHA results on the bedrock tops. The Duqm area mostly features low amplifications, below 1.3 for the considered spectrum. Surface ground-motion maps show low hazard values with Peak Ground Accelerations (PGA) vary between about 2 and 5% g for a 475-year return period. Although several sites are assessed to be susceptible to liquefy, liquefaction analyses indicate that surface ground motions for a 475-year return period are insufficient to produce liquefaction.

Nonlinear soil effects on observed and simulated response spectra

AbstractSoil effects are collectively referred to the influences that local geology and morphology of soil deposits have on ground motions coming from bedrock. The quantification of soil effects in building codes has a great impact in the design of structures because soil factors amplify the reference seismic input, which is typically defined for rock‐type soil class from probabilistic seismic hazards analysis. This topic, within earthquake engineering, represents one of the typical interfaces between structural engineering, geotechnical engineering and engineering seismology. In fact, this issue is generally addressed with different approaches depending on the background of the researchers. This article investigates soil effects combining the viewpoints of structural and geotechnical engineers and seismologists. It is shown that the averaging technique adopted for the definition of ground motion predictive models for spectral ordinates does not play a significant role in defining the results of rock‐like soil classes. However, for other soil classes characterized by soil effects, different methods of averaging the spectral ordinates produce significant differences. The main result of this study is the proposal of a new analytical formulation for the quantification of soil amplification factors for both acceleration and displacement response spectra. The proposed formulation is based on a database of real ground motions and simulated accelerograms. The latter have been obtained through stochastic ground response analyses, with the propagation of natural ground motions on rock‐like soil class through randomly generated soil deposits representative of different soil classes of Eurocode 8 and the Italian Building Code. The comparison between real and simulated data revealed the crucial role of soil nonlinearity in the definition of soil effects, which is also in relation with the variation of magnitude, fault distance and the intensity measures expected on outcropping rock.

A simplified procedure for predicting the soil amplification factor based on the strain compatible period

This paper proposed a simplified procedure for predicting the amplification factor based on a new empirical model for estimating the site period considering nonlinear strain range of soil. The analysis results suggested the depth to bedrock of the soil profile affects the site period at certain shaking intensity levels. Considering this finding, we first proposed a new empirical model to estimate the site period by propagating 78 input motions through 119 soil profiles. A statistical method confirmed the accuracy of the proposed empirical method, which represents the effect of both dynamic properties of soil and input motion features on site response. We then presented a simplified procedure for predicting the amplification factor by taking to account the site period shift and soil nonlinear behavior due to the interaction of damping increase and the resonance controlling effect. Finally, the accuracy of the simplified procedure results in predicting the amplification factor was evaluated by considering the equivalent linear and nonlinear approaches. The results revealed that the simplified model captures the trends of equivalent linear site response analyze in predicting the amplification factor with acceptable accuracy.

Modelling of soil-structure interaction in OpenSees: A practical approach for performance-based seismic design

In this paper, a numerical tool based on the Monkey-tail fundamental lumped parameter model is proposed for the simulation of dynamic soil-structure interaction (SSI). The proposed model has been implemented in the OpenSees finite element environment where the input parameters are merely function of the soil properties. The ease of use, accuracy and versatility of the proposed model is demonstrated in order to encourage its use within, among others, the practicing engineers’ community. Furthermore, the influence of the SSI and local soil conditions (i.e., site effect) on the seismic response of two 5-storey steel moment-resisting frame buildings has been investigated. Preliminary results shed light on the influence of these two geotechnical aspects on the structural seismic response where peak floor displacements and inter-storey drifts considering the SSI are even larger in the lower stories than those of the fixed base case. Furthermore, the results revealed the dependence of the soil amplification factor on the fundamental period of vibration, seismic intensity level and soil stiffness which are not taken into account by the current European design codes.

A preliminary proposal towards the revision of Indian seismic code considering site classification scheme, amplification factors and response spectra

This paper aims to improve the site classification scheme and amplification factors for the Indian Seismic Code. The present code IS 1893 (1):2016 ignores the amplification of effective peak ground acceleration due to the existence of soft soil layers. This results in lower design spectral accelerations on soil sites compared to those adopted by codes in other nations. 124 well documented sites from India are considered for ground response analysis using the equivalent linear procedure of DEEPSOIL. Time histories recorded from India and abroad are made spectrum compatible with the Type I spectra of Indian code, corresponding to all the seismic intensities with Effective Peak Ground Acceleration of 0.1 g, 0.16 g, 0.24 g and 0.36 g. Statistical methods are used to construct mean, mean plus standard deviation and mean minus standard deviation response spectra and amplification factors for the sites considered. Before the statistical analysis, each amplification factor curve is normalized with the effective site period (Tg) which exhibits a “characteristic peak at values of T/Tg not far from 1”. Normalized acceleration response spectra as well as period dependent soil amplification factors and equations are proposed for the new classification system. It is observed that the stratigraphy, impedance contrast, sediment thickness and site period play an important role in determining the soil amplification factors and therefore, should be considered in the future site classification schemes of the Indian Seismic Code.

Seismic stability analysis of tunnel face in purely cohesive soil by a pseudo-dynamic approach

To give a solution for seismic stability of tunnel faces subjected to earthquake ground shakings, the pseudo-dynamic approach is originally introduced to analyze tunnel face stability in this study. In the light of the upper-bound theorem of limit analysis, an advanced three-dimensional mechanism combined with pseudo-dynamic approach is proposed. Based on this mechanism, the required support pressure on tunnel face can be obtained by equaling external work rates to the internal energy dissipation and implementing an optimization searching procedure related to time. Both time and space feature of seismic waves are properly accounted for in the proposed mechanism. For this reason, the proposed mechanism can better represent the actual influence of seismic motion and has a remarkable advantage in evaluating the effects of vertical seismic acceleration, soil amplification factor, seismic wave period and initial phase difference on tunnel face stability. Furthermore, the pseudo-dynamic approach is compared with the pseudo-static approach. The difference between them is illustrated from a new but understandable perspective. The comparison demonstrates that the pseudo-static approach is a conservative method but still could provide precise enough results as the pseudo-dynamic approach if the value of seismic wavelengths is large or the height of soil structures is small.

Site Characterization Using Microtremor Array and Seismic Hazard Assessment for Jakarta, Indonesia

AbstractSite characterization is one of the most important components in seismic hazard analysis because it accounts for the important effects of near‐surface geology on ground motion. It is usually quantified based on the time‐averaged S‐wave velocity (VS) for the top 30 m of the profile (VS30). In this study, we estimate the site class in Jakarta based on VS structure estimated using microtremor array observations. The results show that microtremor‐derived VS profiles agree well with standard penetration test‐derived profiles at nine sites. The site‐class estimates in the Jakarta area can be divided into two National Earthquake Hazards Reduction Program classes: (a) site class E (soft soil) located in alluvium, beach ridge, and alluvial fan deposits in northern and western Jakarta, and (b) site class D (stiff soil) found mainly in alluvial fan deposits in southeastern Jakarta. The variation of VS30 in Jakarta leads to different soil amplification factors that will impact the seismic hazard at the surface. We show that the seismic hazard resulting from selected ground‐motion models (GMMs) illustrates a clear influence of site effects at long periods (>1 s). However, the effect on peak ground acceleration and response spectra for short periods (0.2 s) appear to be less pronounced, due to the GMMs’ treatment of basin effects and nonlinear soil behavior. Available GMMs may not accurately account for such effects in the Jakarta basin, and GMMs specific to Indonesia should be developed to accurately assess seismic hazard there.

Pseudo-Dynamic Approach to Analyze the Seismic Stability of Reinforced Soil Wall for c–ϕ Soil Backfill

In the design of reinforced soil wall, soil is considered as cohesionless. In earthquake-prone regions, analysis is based on either pseudo-static or pseudo-dynamic approach. Very few studies have considered behavior of reinforced soil walls assuming c–ϕ soil backfill in the pseudo-dynamic approach. Present study is aimed to investigate the seismic stability of reinforced soil wall incorporating the pseudo-dynamic approach. The propagation of primary and shear waves is considered under both horizontal and vertical seismic accelerations incorporating effect of soil amplification. A numerical algorithm is proposed to obtain the required strength of reinforcements, critical angle of failure wedge, and factor of safety of the reinforced soil wall for specific number of reinforcement layers and length of reinforcement. The effects of shear strength parameters, coefficients of ground accelerations, and soil amplification factor on the stability of the reinforced soil wall are critically examined. Variation in the mobilized pullout resistance of reinforcement layers and associated factor of safety with time is considered in the assessment of stability. For c–ϕ soil backfill, numerical predictions are in good agreement when compared with available studies in the literature for validation purpose.

An investigation on the evaluation of dynamic soil characteristics of the Elazig City through the 1-D equivalent linear site-response analysis

Consideration of the effects of the site response in the design of civil structures systems is of important to mitigate the damages to a certain extent on structures and the environment. Hence, it is relatively crucial to reliably attain the dynamic soil parameters of an earthquake-prone city/state. In the current study, a comprehensive investigation on the dynamic soil properties of the city of Elazig with very close proximity to the East Anatolian Fault Zone (EAFZ) having a high potential of producing destructive earthquakes is carried out. Performing probabilistic seismic hazard analysis (PSHA), the moment magnitude of the city is determined as Mw = 7.7 according to 10% probability of exceedance in 50 years. Bedrock-level acceleration spectra is developed utilizing different attenuation relationships for the city, and 1-D equivalent linear site response analysis is conducted on an example soil profile of the city through the SHAKE2000 software considering 16 earthquake motions recorded at the bedrock level. Local surface acceleration spectra obtained from the analysis are then compared to the design spectra of the Turkish Seismic Code for Buildings (TSCB) and Eurocode-8 (EC8) in an attempt to identify the difference between the code spectra and local surface spectra. In addition, in situ geotechnical tests of standard penetration and seismic refraction are conducted at different locations of the study area. Incorporating the results from the field tests into the site response analysis, the soil amplification factor, predominant soil period, peak ground acceleration and spectral maps for the period of T = 0.2 and T = 1.0 s are obtained for the study area. The outcomes from the analysis reveals that structures with higher vibration period than T = 1.0 s are subjected to lower spectral acceleration (Sa), whereas higher Sa values can be used for those with a vibration period lower than T = 0.2 s.

Practical seismic microzonation in complex geological environments

The seismic design of buildings and infrastructure components requires the estimation of the hazard considering the dynamic response of the soil deposits, which substantially modifies the characteristics of the input motion at the rock basement. Seismic microzonation studies attempt to identify geologic zones of an area of interest with similar seismic hazard at a local scale. This paper presents a methodology to obtain seismic spectral amplification factors within each soil zone characterization considering the main sources of uncertainty. Results are presented in terms of spectral amplification factors for various seismic intensities and soil profile vibration periods. Design soil amplification factors can then be mapped using the measured vibration period of the soil profile at each location and the seismic intensity at bedrock for a given design return period. Response and design spectra may then be estimated at surface level for every location. Results can be easily integrated into probabilistic risk assessment platforms such as CAPRA (www.ecapra.org) for hazard and risk evaluations.

Re-evaluation of code-specified stratigraphic amplification factors based on Italian experimental records and numerical seismic response analyses

For several engineering and seismological applications, site effects can be synthetically evaluated as a soil amplification factor of the reference ground motion on a rock outcrop leading to the peak ground acceleration and/or the response spectrum expected at a soil site, classified according to its equivalent shear wave velocity, VS,30. In this work, nonlinear stratigraphic amplification factors as specified by Eurocode 8 (EC-8) and National Technical Code (NTC) were assessed with reference to selected accelerometric records of the Italian seismic network and well-characterized recording stations classified according to VS,30. A first set of ‘empirical’ amplification factors has been identified, by selecting those stations on deformable soil for which records of the same events exist also at a nearby reference station located on outcropping rock (4 sites, 102 records). A second set of ‘semi-empirical’ data has been obtained by analysing the accelerograms recorded at stations where the geotechnical characterization was comprehensive and the reference motion could be back-figured by de-convolution to the bedrock (7 sites, 50 records). A third set of ‘analytical’ data was obtained from 1D numerical simulations of seismic site response performed on virtual stratigraphic profiles, consistent with the ground classification adopted by EC-8 and NTC, and subjected to 80 acceleration time histories of 22 Italian earthquakes, recorded at 19 stations of the Italian Network classified as rock sites. Empirical, semi-empirical and analytical data have been therefore integrated to express the stratigraphic amplification factor of peak ground acceleration and spectral intensity as a function of the corresponding reference ground motion value for each class of subsoil.